Table 1.
Comparison of 123I-IMP and 99mTc-ECD
| 123I-IMP | 99mTc-ECD | |
|---|---|---|
| Pharmacokinetics | Brain accumulation increases gradually after administration, peaking and stabilizing at 20–30 min, as most accumulates in the lungs after intravenous injection and is gradually released into the arterial blood | Brain accumulation is fixed and stabilized in about 2 min as it is metabolized from fat-soluble to water-soluble after passage through BBB and retained in the brain |
| Emergency scan | Unavailable | Available from 99Mo/99mTc generators |
| T1/2 | 13.2 h | 6.01 h |
| Principal energy | 159 keV | 141 keV |
| Image quality |
Slightly inferior – Limited dosage (111–222 MBq) – Higher energy gamma-rays than 159 keV |
Better – Higher dosage (370–740 MBq) |
| Correlation with perfusion |
Better – Higher first-pass extraction fraction (> 90%) |
Underestimation in high-flow areas – Lower first-pass extraction fraction (77%) |
| Quantification |
Autoradiography method Graph plot |
Patlak plot |
| Procedure | Scan 20 min after injection | Scan 5 min after injection |
123I-IMP N-isopropyl-(123I)-p-iodoamphetamine, 99mTc-ECD technetium-99 m ethyl cysteinate dimer